Direct rendering of textured height fields

• US 5,579,456 A
• Filed: 11/29/1995
• Issued: 11/26/1996
• Est. Priority Date: 10/15/1993
• Status: Expired due to Term

• Current Assignee: Rockwell Collins Simulation and Training Solutions, LLC (Rtx Corporation)
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Cosman, Michael A.
• Primary Examiner(s): Herndon, Heather R.
• Assistant Examiner(s): BUCHEL JR, RUDOLPH JOHN
• Application Number:
  US08/564,820
• Time in Patent Office: 363 Days
• Field of Search: 395/119, 395/121, 395/127-129
• US Class Current: 345/419
• CPC Class Codes: G06T 15/20 Perspective computation
• CPC Class Codes: G06T 17/05 Geographic models

Abstract

To create a dynamic textured display, images of textured height fields (elevation samples arrayed on a rectangular coordinate grid, as to represent a terrain) are rendered, the system performing an initial pass that re-samples the height-field data into a radial form and a subsequent pass using the radial data to create textured, shaded picture elements (pixels) for an instantaneous field of view. Thus, texturing, shading, blending and scan conversion complete the pixel processing to drive a display unit. The system is particularly applicable to the generation of dynamic perspective images of terrain. The process provides pixel-limited textural resolution in the final image with effective antialiasing of internal and horizontal silhouette edges.

Claims

1. A process for producing a perspective image based on height field data, said image having a foreground and a background, said process comprising the steps of:

establishing a centered viewpoint for said perspective image;

sampling said height field data to generate a radial form height field, said height field having a relatively greater level of detail for said foreground and a relatively lesser level of detail for said background, said sampling step including;

defining rays extending radially from said centered viewpoint in model space, said rays being substantially parallel in image space; and

sampling said height field data at selected locations along said rays in model space to provide height samples, said locations forming vertices of substantially square trapezoidal shapes in model space, said shapes increasing in size with increasing radial distance from said centered viewpoint in model space, but being substantially uniform in image space;

processing picture elements in relation to said viewpoint based on said radial form height field to provide perspective display data; and

driving a display in accordance with said perspective display data to provide said perspective image.

2. A process according to claim 1 wherein said step of sampling said height field data includes defining a system of azimuth and range coordinates such that adjacent sets of said coordinate points define said substantially square trapezoidal shapes.

3. A process according to claim 1 wherein said step of processing picture elements includes defining and interconnecting a system of azimuth and range coordinates to provide polygons.

4. A process according to claim 3 wherein said polygons are defined as triangles.

5. A process according to claim 3 wherein said picture elements are processed by combining values selectively from said polygons proximate each picture element.

6. A process according to claim 1 wherein said step of processing said picture elements further includes texturing said picture elements.

7. A process according to claim 1 wherein said step of processing said picture elements further includes shading said picture elements.

8. A process according to claim 1 wherein said step of processing said picture elements further includes scan converting said picture elements to a raster display format.

9. A process according to claim 1 wherein said step of sampling said height field data includes defining a system of azimuth and range coordinates such that adjacent sets of said coordinate points define said substantially square trapezoidal shapes to provide polygons and wherein said picture elements are processed by combining values selectively from said polygons proximate each picture element and further, texturing said picture elements, shading said picture elements and scan converting said picture elements.

19. A process according to claim 1 wherein said height samples form vertices of polygons in image space, said image space being defined by a THETA/PHI coordinate system and said step of processing picture elements includes scan-converting said polygons using a PHI-directional filter.

20. A process according to claim 19 wherein radial edges of said polygons are in alignment with said rays in said THETA/PHI image space.

21. A process according to claim 20 wherein said step of processing picture elements includes texturing said polygons in accordance with said radial edges of said polygons.

22. A process according to claim 20 wherein said step of processing picture elements includes rendering anti-aliased ridgelines in said image space in accordance with said radial edges of said polygons.

23. A process according to claim 21 wherein said step of texturing involves MIP-map, an appropriate level of which is selected in accordance with said radial edges of said polygons.

24. A process according to claim 22 wherein said step of rendering anti-aliased ridgelines includes generating a PHI list based on said radial edges of said polygons.

25. A process according to claim 1 wherein said height samples form vertices of polygons in image space defined by a THETA/PHI coordinate system and said step of processing said picture elements includes determining which of said polygons influence said picture elements.

26. A process according to claim 1 wherein said height samples are addressed in a THETA/PHI coordinate system and each includes an X-Y position in said height field data and a filtered Z-height.

10. A system for producing perspective images having a foreground and a background with respect to a selected viewpoint, as of a terrain, comprising:

memory means for storing a height field, as to represent a terrain;

radial means for providing radial height field data from said memory means in a re-sampled radial coordinate form, said re-sampled radial coordinate form providing a relatively greater level of detail for said foreground and a relatively lesser level of detail for said background and defining;

rays extending radially from said viewpoint in model space, said rays being substantially parallel in image space; and

selected re-sampling locations along said rays in model space providing re-sampled heights, said locations forming vertices of substantially square trapezoidal shapes in model space, said shapes increasing in size with increasing radial distance from said centered viewpoint in model space, but being substantially uniform in image space;

an image generator means including a pixel processor for receiving said radial height field data from said radial means to formulate display pixel data indicative of said height field with respect to said selected viewpoint; and

display means for receiving said display pixel data to display said perspective representation.

11. A system according to claim 10 wherein said radial means comprises means to access said memory means to receive height field data and re-sample said height field data into radial height field data based on azimuth and range coordinates.

12. A system according to claim 11 wherein said radial means further includes means for blending values of said height field data to provide values of said radial height field data.

13. A system according to claim 10 wherein said image generator means includes means to formulate polygons representative of terrain skin whereby to formulate said display pixel data.

14. A system according to claim 13 wherein said image generator means further includes means to texture said display pixel data.

15. A system according to claim 13 wherein said image generator means further includes means to shade said display pixel data.

16. A system according to claim 13 wherein said image generator means further includes means to scan convert said display pixel data.

17. A system according to claim 13 wherein said image generator means further includes means for processing individual pixels for said perspective representation with respect to said polygons contiguous to each pixel.

18. A system according to claim 17 wherein said image generator means further includes filter means for blending values from said polygons.